More than 26 people have been killed in a wave of bombings in two mainly Shia districts of Baghdad, according to police and hospital sources.

The first of the attacks happened in Sadr City, in the north-east of the Iraqi capital. One bomb was planted on a parked motorcycle and the other was a roadside device, a police source told Reuters. At least 12 people were killed.

"There was a group of day labourers gathered, waiting to be hired for work. Someone brought his small motorcycle and parked it nearby. A few minutes later it blew up, killed some people, wounded others and burned some cars," a police officer at the scene said.

A Reuters reporter said there were bloodstains around the scene of the motorcycle bomb attack, and tarmac on the road had been ripped up by the explosion. Building tools and shoes were scattered across the site.

Half an hour later, a roadside bomb exploded near a small tea shop in the same neighbourhood, killing one person. Police said they found and defused two other bombs.

Less than two hours after that, two blasts hit the Shia district of Kazimiya, in the north of the city, killing 14 people.

Officials said the blasts happened almost simultaneously, with at least one caused by a car bomb. At least 60 people were injured.

Iraq is still plagued by a deadly Sunni Muslim insurgency and Shia militias nearly nine years after the US-led invasion.

On Wednesday, deadly attacks targeted the homes of police officers and a member of a government-allied militia. Those attacks, in the cities of Baqouba and Abu Ghraib, outside Baghdad, killed four people, including two children, officials said.

"People have real fears that the cycle of violence might be revived in this country," Tariq Annad, a government employee who lives near the site of the Sadr City attacks told the Associated Press.

A political crisis that erupted shortly after US troops withdrew from Iraq on 18 December has revived concerns about sectarian violence in Iraq, which teetered on the brink of civil war in 2006-07.

The Iraqi prime minister, Nuri al-Maliki, a Shia, angered rivals when he asked parliament to have his Sunni deputy, Saleh al-Mutlaq, removed and sought an arrest warrant for the Sunni vice-president, Tareq al-Hashemi, on charges that he ran death squads.

On Tuesday, members of the Sunni-backed Iraqiya bloc boycotted Iraq's parliament and cabinet, accusing Maliki's bloc of governing alone in a power-sharing coalition that had been supposed to ease sectarian tensions.

A spate of bombings that killed 72 people in mainly Shia areas of Baghdad a few days after the political crisis began deepened fears over rising sectarian tensions.

The inclusion of Iraqiya in the governing coalition was widely considered crucial to prevent a return to the kind of sectarian violence unleashed after the 2003 invasion in which thousands were killed.

Many Sunnis have complained of being sidelined in the political process since Saddam Hussein was ousted and the majority Shia dominated the government.